KR20080064817A - Multigas monitoring and detection system - Google Patents

Abstract

A spectroscopic detection system is described for monitoring ambient air for toxic chemical substances. The system can be a compact, portable multiple gas analyzer capable of detecting and discriminating a broad range of chemical constituents including various nerve and blister agents as well as toxic industrial chemicals at low or sub part per billion (ppb) levels. The system minimizes false alarms (e.g., false positives or negatives), features high specificity, and can operate with response times on the order of a few seconds to a few minutes, depending on the application. The system can be an entirely self-contained analyzer, with a Fourier Transform Infrared (FTIR) spectrometer, a gas sample cell, a detector, an embedded processor, a display, power supplies, an air pump, heating elements, and other components onboard the unit with an air intake to collect a sample and an electronic communications port to interface with external devices.

Description

Multigas Monitoring And Detection System

FIELD OF THE INVENTION The present invention generally relates to absorption spectrometers, and more particularly to detecting trace amounts of chemical agents, toxic industrial chemicals, and other trace compounds that can be found in ambient air.

Spectroscopy is a study of the interaction between electromagnetic radiation and a sample (including one or more of gas, solid, and liquid). The manner in which radiation reacts with a particular sample depends on the nature of the sample (eg, molecular composition). In general, as radiation passes through the sample, a particular radiation wavelength is absorbed by the molecules in the sample. The particular wavelength of radiation absorbed is specific to each molecule in a particular sample. By identifying which wavelength of radiation is absorbed, it is possible to identify specific molecules present in the sample.

Infrared spectroscopy is a special field of spectroscopy where, for example, the type of molecule in a sample and the concentration of individual molecules are determined by exposing the sample (eg, gas, solid, liquid, or combination thereof) to infrared electromagnetic energy. In general, infrared energy is considered electromagnetic energy with a wavelength of energy between about 0.7 μm (frequency 14,000 cm ⁻¹ ) and about 1000 μm (frequency 10 cm ⁻¹ ). Infrared energy is directed through the sample, and the energy interacts with molecules in the sample. Energy passing through the sample is detected by a detector (eg, an electromagnetic detector). The detected signal is then used, for example, to determine the molecular composition of the sample and the concentration of particular molecules in the sample.

One particular type of infrared spectrometer is the Fourier Transform Infrared (FTIR) spectrometer. This spectrometer is used in various fields such as air quality monitoring, explosives and biological drug detection, semiconductor processing, and chemical production. Other applications for FTIR spectrometers require different detection sensitivities to allow the user to distinguish the molecules present in the sample and to determine the concentration of other molecules. In some applications, it is necessary to identify the concentration of individual molecules in the sample to within about 1 part per billion (ppb). As industrial applications call for greater sensitivity, through optimization of existing spectroscopy systems and the use of new spectroscopy components, the system can repeatably and reliably analyze the lower concentrations of molecules in a sample.

The present invention features in various embodiments a spectroscopic detection system that monitors and / or detects toxic chemicals in a gas sample, such as ambient air. The system detects a wide range of chemical constituents, including various chemical warfare agents (CWAs), toxic organic compounds (TOCs), and toxic industrial chemicals (TICs) at low or sub-ppb levels. And a number of compact and portable gas analyzers that can be distinguished. The system minimizes alarm errors (eg, false positives or negatives), provides high specificity, and can operate with response times of seconds to minutes, depending on the application.

In one embodiment, the system is a restrained automated unit that can be deployed in the building's air handling system to provide a high-speed sensitive threat alert sufficient to protect building occupants and also allow the adaptive infrastructure system to respond to the presence of contaminants. Can be packaged as. In one embodiment, the unit comprises an FTIR spectrometer, a gas sample cell, a detector, an embedded processor, a display, a power supply, an air pump, a heating element, and other components and external devices with air inlets for collecting the sample. It can be an entirely self-contained analyzer with an electronic communication port for its interface.

In one aspect, the invention features a trace gas measurable device. The apparatus includes a source of a first radiation beam and an interferometer for receiving the first radiation beam from the source and forming a second radiation beam comprising an interference signal. The sample cell is in optical communication with the interferometer, the sample cell comprising a concave reflective field surface at the first end of the sample cell and a concave reflective objective surface that is substantially spherical at the second end of the sample cell at the field surface. The objective plane and the field plane are in opposition, and the objective plane is at least one plane to maximize throughput of the second radiation beam propagating through the sample cell through multiple reflections in each of the field plane and the objective plane. Including a cylindrical component to increase the focus match. The apparatus also includes a flow mechanism for forming a flow of a sample of gas through the cell sample, a cooled detector in optical communication with the sample cell, and a processor in electrical communication with the cooled detector. The cooled detector receives an interference signal that propagates through a sample in the sample cell, and the processor determines an absorption profile for the trace gas in the sample from the interference signal. The source, the interferometer, the sample cell, the cooled detector and the processor may be disposed in a housing.

In another aspect, the invention features a method of optically measuring a trace gas. The method includes providing a portable absorption spectrometer comprising a sample cell comprising a field surface at a first end and an object surface at a second end in opposition to form a folded path, and a sample of ambient air Flowing through the cell sample. Optimize the volume of the sample cell and the number of paths of the radiation beam in the folded path to maximize the throughput of the radiation beam propagating within the sample cell to detect trace gases having a concentration of less than about 500 ppb in the sample of ambient air. Can be.

In another aspect, the invention features a method of optically measuring a trace gas. This method provides an absorption spectrometer comprising a substantially closed sample cell. The sample cell includes a field surface at the first end and an object surface in opposition to the second end to direct the radiation beam through the sample cell. The first signal of the radiation beam propagating through the sample of ambient air is measured at the first pressure in the sample cell. The sample cell is pressurized with ambient air until the second pressure is reached, and the second signal of the radiation beam propagating through the sample of ambient air at the second pressure is measured. The first signal and the second signal are combined to determine a signal indicative of the presence of trace gas.

In various embodiments, the first signal and the second signal can be combined to determine an absorption profile for trace gas. In some embodiments, an absorption profile for the trace gas can be determined from an interfering signal propagating through the sample in the sample region. In one embodiment, by applying pressure to the sample cell, the amplitude of the absorption profile of the trace gas can be increased relative to a baseline signal.

In another aspect, the invention features a method of removing contaminants from an optical system. The method includes determining a concentration of a contaminant in at least one sample region of an absorption spectrometer, and if the concentration of the contaminant exceeds a contamination value, heating the sample region to a purge temperature to remove the contaminant. Steps. The concentration of the contaminant is monitored while heating the sample region, and heating of the sample region can be reduced or stopped when the concentration of the contaminant reaches a purification value.

In another aspect, the invention features a trace gas measurable device. The apparatus comprises an interferometer for receiving a first radiation beam from a source and forming a second radiation beam comprising an interference signal, a sample cell in optical communication with the interferometer, and a flow mechanism for forming a flow of a sample of gas through the cell sample A module for heating at least the sample cell, a detector in optical communication with the sample cell, and a processor in electrical communication with the detector and the module. The detector receives an interference signal that propagates through a sample in the sample cell. The processor determines the concentration of contaminants in the sample from the interference signal and heats the sample cell to a purge temperature to remove the contaminants when the concentration of contaminants in the sample cell exceeds a contamination value. And monitor the concentration of the contaminant while the module heats the sample cell and signal the module to reduce or stop heating of the sample cell when the concentration of the contaminant reaches a purification value.

In another example, any of the above aspects or the apparatus or method described herein can include one or more of the following features. In various embodiments, the trace gas has a concentration of less than about 500 ppb. In one embodiment, the trace gas has a concentration between about 10 ppb and about 50 ppb. In one embodiment, the housing is portable and defines a hole for intake of ambient air containing a sample of the gas. The aperture may be in fluid communication with the sample cell. In one embodiment, the sample cell may have a volume of less than about 0.8 liters.

In some embodiments, the sample cell can have a path length between about 5 meters and about 12 meters. In one embodiment, the apparatus further comprises a heating element disposed in the portable housing to heat at least the sample cell to a temperature between about 40 ° C. and about 180 ° C.

In some embodiments, the housing is mountable to a building air treatment system. An alarm may sound to alert the presence of contaminants in the air treatment system.

In one embodiment, the sample of gas flows through the sample cell at a flow rate greater than about 3 liters per minute. The sample cell may have a gas exchange rate between about 80% and about 95% at time intervals of about 10 seconds. In one embodiment, the sample of gas comprises a chemical agent, a toxic inorganic compound, or a toxic organic compound. The device may have a response time of less than about 20 seconds for about 50 ppb of at least one of sarin, starch, cattle, sulfur mustard, and VX.

In various embodiments, the first absorption spectrum may be measured at a first resolution and the second absorption spectrum may be measured at a higher resolution to detect the trace gas.

In various embodiments, the field surface may comprise a concave reflective surface, and the objective surface may include a substantially spherical concave reflective surface. The objective may include a cylindrical component that increases focus agreement in at least one plane to maximize throughput of the radiation beam propagating through the folded path of the sample cell. In one embodiment, an absorption profile for the trace gas may be determined from an interference signal propagating through the sample in the sample region.

Other aspects and advantages of the invention will be apparent from the following drawings, detailed description, and claims that illustrate, for example, the principles of the invention.

The advantages of the present invention described above will be better understood by reference to the following detailed description taken in conjunction with the accompanying drawings, along with other advantages. In the drawings, like reference characters generally refer to like parts throughout the different figures. The drawings are not necessarily drawn to scale, but instead generally focus on the principles of the invention.

1 is a block diagram of an exemplary detection system for monitoring and / or detecting trace gas in a gas sample in accordance with the present invention.

2 is a schematic diagram of an exemplary optical configuration in accordance with the present invention.

3 is a block diagram of an exemplary flow system for introducing a sample into a sample cell in accordance with the present invention.

4 is a graph of path length / NEA versus number of passages between optical surfaces of a sample cell in accordance with the present invention.

5 is a graph of trace gas concentration versus time during input of trace gas to an exemplary detection system in accordance with the present invention.

6 shows a time line for a series of measurements according to the invention.

7 is a plan view of an exemplary detection for monitoring and / or detecting trace gas in a gas sample in accordance with the present invention.

8 is a plan view of some components of exemplary detection for monitoring and / or detecting trace gas in a gas sample in accordance with the present invention.

1 shows a block diagram of an exemplary apparatus 10 for monitoring and / or detecting trace gas in a gas sample. Device 10 may be used to detect trace amounts of substances such as sarin, tabun, soman, sulfur mustard, and VX nerve gas. In some embodiments, vapors of solid or liquid materials may be detected. The device 10 may be an absorption spectrometer and / or a Fourier Transform Infrared (FTIR) spectrometer. In the illustrated embodiment, the device 10 includes a source 14, an interferometer 18, a sample cell 22, a source of a gas sample 26, a detector 30, a processor 34, a display 38, And a housing 42. In various embodiments, the device 10 may be used to detect the trace amount of gas in a short time period while reducing false positives or negatives if possible.

In various embodiments, source 14 may provide a radiation beam (eg, an infrared radiation beam). Source 14 may be a laser or an incoherent source. In one embodiment, the source is a glowbar, an inert solid that is heated to about 1000 ° C. to generate blackbody radiation. The globa can be formed of silicon carbide and can be electrically powered. The spectral range of the system may be between about 600 cm ⁻¹ and about 5000 cm ⁻¹ . It may be between ¹ and about 4 cm ^{-1 -} the system resolution is 2 cm. In one embodiment, the detection system may record a higher resolution spectrum of the trace gas upon detection of the trace gas. Higher resolution spectra can help identify trace gases.

In various embodiments, radiation source 14 and interferometer 18 may comprise a single instrument. In some embodiments, interferometer 18 is a Michelson interferometer commonly known in the art. In one embodiment, interferometer 18 is a BRIK interferometer available from MKS Instruments, Inc. (Wilmington, Mass.). BRIK interferometers combine combiners that separate and combine input radiation, moving corner cubes that modulate radiation, white light sources used to identify center bursts, and VCSELs that monitor the speed of corner cubes. Cavity Surface Emitting Laser). BRIK interferometers may not be affected by thermal changes as well as tilt and lateral motion errors, which may improve the ruggedness of the interferometers.

In one embodiment, interferometer 18 may be a module including a radiation source, a fixed mirror, a movable mirror, an optical module, and a detector module (eg, detector 30). An interferometer module can measure all optical frequencies generated by its source and transmitted through a sample (eg, sample 26 contained within sample cell 22). The radiation is directed to an optical module (eg an optical splitter) capable of splitting the radiation into two beams, a first signal and a second signal. The movable mirror produces a variable path length difference between these two initially substantially identical beams of electromagnetic energy. Movable mirrors are usually moved or passed at a constant speed. After the first signal has moved a distance different from the second signal (in this embodiment, due to the movement of the movable mirror), the first and second signals can be recombined by the optical module, thus A radiometric signal is produced with an intensity modulated by the interference of the beam. This interfering signal passes through the sample and is detected by the detector. The presence of other samples (eg, solids, liquids, or gases) can modulate the intensity of the radiation detected by the detector. Therefore, the output of the detector is a time dependent signal that varies with the optical path difference formed by the relative positions of the fixed mirror and the movable mirror as well as the modulation of the electromagnetic signal generated by the sample. This output signal can be described as an interferogram.

The degree of interference can be expressed in terms of the received energy intensity versus the position of the movable mirror. Those skilled in the art view interference as a signal that is a function of time. The degree of interference is a function of the variable optical path difference produced by the displacement of the movable mirror. Since the position of the movable mirror usually and preferably passes at a constant speed, those skilled in the art regard the interference as a "time domain" signal. Interference can be understood as the sum of all wavelengths of energy emitted by the source and passing through the sample. Using a mathematical process called Fourier Transform (FT), a computer or processor can transform interference into a spectrum that is characteristic of light absorbed or transmitted through the sample. Because individual types of molecules absorb specific wavelengths of energy, it is possible to determine the molecule (s) present in the sample based on the degree of interference and the corresponding spectrum. In a similar manner, the amount of energy absorbed or passed by the sample can be used to determine the concentration of molecule (s) in the sample.

In various embodiments, the interferometer is not used to form the interfering signal. Absorption spectrometers are used to record the optical signal, and information about the trace species is derived from the signal transmitted through the sampling area. For example, absorption spectrum or differential spectrum may be used.

In various embodiments, sample cell 22 may be a folded path and / or a multipath absorbing cell. Sample cell 22 may include an aluminum housing that houses a system of optical components. In some embodiments, sample cell 22 is a folded-path optical analysis gas cell as described in US Pat. No. 5,440,143, which publication is incorporated herein by reference.

In various embodiments, the source of the sample 26 of gas may be ambient air. The sample cell 22 or gas sampling system may collect ambient air and introduce it into the sampling area of the sample cell 22. Samples of gas may be introduced into the sample cell 22 at a predetermined flow rate using a flow system comprising an inlet 46 and an outlet 50 of the sample cell 22.

In various embodiments, the detector 30 may be an infrared detector. In some embodiments, the detector 30 is a cooled detector. For example, the detector 30 may be a cryogen cooled detector (eg, a mercury cadmium telluride (MCT) detector), a Stirling cooled detector, or a Peltier cooled detector. In one embodiment, the detector is a deuterated triglycine sulfate (DTGS) detector. In one embodiment, the detector is a 0.5 mm sterling-cooled MCT detector with a 16-μm cutoff that can provide the sensitivity needed to detect trace gases. The relative responsitivity (ie, the ratio of the response as a function of wavelength) of a sterling-cooled MCT detector is at least 80% over the main wavelength region of interest (eg, 8.3-12.5 μm). In addition, Stirling - D * value of-cooled MCT detector may be at least ^{3x10 10 cm Hz 1/2 W} -1. D * may be defined as the inverse of the product of detector noise equivalent power and the square root of the active element region.

Processor 34 may receive a signal from detector 30 and identify the trace gas by its spectral fingerprint or provide a relative or absolute concentration for a particular substance in a sample. The processor 34 may be, for example, signal processing hardware and quantitative analysis software running on a personal computer. Processor 34 may include a processing unit and / or a memory. The processor 34 may continuously acquire and process the spectrum while calculating the concentration of the multiple gases in the sample. The processor 34 may send information to the display 38 such as the identity of the trace gas, the spectrum of the trace gas, and / or the concentration of the trace gas. Processor 34 may store spectral concentration time records in graphical and tabular form and store measured spectra and remaining spectra, which may likewise be displayed. The processor 34 may collect and store various other data for later reprocessing or review. Display 38 may be a cathode ray tube display, a light emitting diode (LED) display, a flat screen display, or other suitable display known in the art.

In various embodiments, housing 42 may be adapted to provide a portable, strong or light detection system. The housing 42 may include a handle and / or may be easily secured to a transport mechanism such as a pullcart or a handtruck. The housing 42 may be strong enough to withstand misalignment of the optical structure or breakage of components when transported or dropped. In various embodiments, the weight of the device 10 may be as small as 40 pounds. In one embodiment, the device 10 is entirely self-contained (e.g., all components necessary to collect a sample, record a spectrum, process a spectrum, and display information about the sample). In the housing 42).

2 illustrates an embodiment of an optical configuration that can be used with the apparatus 10. The radiation beam from the source 14 (eg, a glowbar) is directed by the first mirror 52 to the interferometer 18 (eg, including a potassium bromide light separator). The radiation beam is input into the sample cell 22 by a parabolic mirror PM towards the first collapsible mirror 58. The radiation beam exits the sample cell and is directed by the second fold mirror 62 to an elliptic mirror 66 (EM), which sends the radiation beam to the detector 30.

In one exemplary embodiment, parabolic mirror 54 may have an effective focal length of about 105.0 mm, a parent focal length of about 89.62 mm, and an off center value of about 74.2 mm. . The parabolic mirror 54 may have a diameter of about 30.0 mm and a reflection angle of about 45 °.

In one embodiment, the elliptical mirror 66 may have a major semi-axis of about 112.5, a minor semi-axis of about 56.09, and an inclination angle of an ellipse of about 7.11 °. The diameter of the oval mirror 66 may be about 30.0 mm and the chief ray may be about 75 °.

In various embodiments, the first fold mirror 58 may have a diameter of about 25 mm, and the second fold mirror 62 may have a diameter of about 30 mm.

Mirrors and optical structures may include gold coatings, silver coatings, or aluminum coatings. In one embodiment, the oval and parabolic mirrors are coated with gold and the flat folding mirrors are coated with silver.

In various embodiments, the sample cell may include an objective surface 74 and a field surface 78. The objective surface 74 may be substantially spherical and concave. The field surface 78 may be concave and may be positioned in opposition to the object surface 74. Objective 74 may include at least one cylindrical component that increases the match of focus in at least one plane to maximize the throughput of the radiation beam propagating between the two faces 74, 78. . In one embodiment, objective 74 may include a plurality of substantially spherical and concave reflective objectives, each of which increases focus agreement in at least one plane to maximize throughput of the radiation beam. It may comprise a cylindrical component. The center of curvature (s) of the object surface (s) may be located behind the field surface 78. By increasing focus matching in at least one plane, distortion, astigmatism, spherical aberration, and coma can be better controlled, and higher throughput can be realized. When a cylindrical component is added, the effective radius of curvature is reduced in one plane, so that light incident on the reflective surface can better approach the focal point in the orthogonal plane. In one embodiment, objective 74 has a cylindrical component that is superimposed on it to provide different radii of curvature in two orthogonal planes. Objective 74 may have an appearance similar to a donut.

The overall path length of the sample cell 22 may be between about 5 m and about 15 m, although longer and shorter path lengths may be used depending on the application. In one specific embodiment, the sample cell 22 has a total path length of about 10.18 m due to about 48 total passage numbers between the objective surface 74 and the field surface 78. The optical structure of the sample cell 22 can be optimized for a 0.5-mm detector and 1 steradian collection angle. The detector magnification may be about 8: 1. Objective 74 and field 78 may have a gold coating layer having a nominal reflectance of about 98.5% between 800 cm ⁻¹ and 1200 cm ⁻¹ . The internal volume of the sample cell may be between about 0.2 L and about 0.8 L, but larger and smaller volumes may be used depending on the application. In one specific embodiment, the volume is about 0.45 L.

In one embodiment, the radiation beam is directed through the sample cell 22 with the sample cell 22 directed, focusing the radiation beam on the inlet slit of the sample cell 22, and / or directing the radiation beam to the detector. The mirror and optical structure used to direct the light may be optimized to match the optical characteristics of the sample cell, which may maximize the throughput of radiation and improve the sensitivity of the detection system.

For example, in one embodiment, a properly aligned optical configuration can have an efficiency of about 88.8%. As used herein, the efficiency may be the ratio of the number of rays hitting an image square to the total number of emission rays in the emission angle range. In one embodiment, the positions of the fold mirrors 58 and 62 and the detector 30 are adjustable, thus varying between the interferometer 18, the parabolic mirror 54, the sample cell 22, and the detector 30. Mechanical tolerances can be compensated for. In one embodiment, the following nominal (designed) optical distances may be used to optimize throughput.

Distance (X1) from the detector of about 21.39 mm to the elliptical mirror.

Distance from oval mirror of about 132.86 mm to fold mirror (X2).

Distance (X3) from the fold mirror of approximately 70.00 mm to the sample cell (surface of the field mirror).

Sample cell path length of about 10181.93 mm.

Distance from sample cell of about 70 mm to fold mirror (X4).

Distance from folding mirror of approximately 35 mm to parabolic mirror (X5).

3 shows an embodiment of an example flow system 82 for introducing a sample into a sample cell 22. Flow system 82 includes a filter 86, a flow sensor 90, an optional heating element 94, a gas cell 22, a pressure sensor 98, a valve 102, and connected by a gas line 110, and Pump 106. Arrows indicate the direction of flow. One or more of the flow system 82 components are wetted such as, for example, Teflon, stainless steel, and Kalrez to withstand decontamination temperatures and the corrosive properties of CWA and TIC. parts).

Filter 86 may be an inline 2 μm stainless steel filter available from Mott Corporation (Farmingstone, Connecticut, USA). Flow sensor 90 may be a mass flow sensor comprising stainless steel wetted parts, such as the flow sensor available from McMillan Company (Georgetown, Texas, USA). The heating element 94 may be a line heater available from Watlow Electric Manufactuing Company (St. Louis, Missouri, USA). The pressure sensor 98 may be a Baratron pressure sensor available from MKS Instruments, Wilmington, Massachusetts. The valve 102 can be stainless steel and can include a Teflon o-ring, such as a valve available from Swagelok (Solo, Ohio). Gas line 110 may be a 3/8 '' diameter tubing available from Swagelok.

The pump 106 can be a "micro" diaphragm pump with a heated head. Dia-Vac B161 pumps available from Air Dimensions, Inc., Deerfield Beach, FL, USA may be used. In one embodiment, a small diaphragm pump available from Hargraves Technology Corporation (Moorsville, North Carolina, USA) may be used. In this embodiment, the pump 106 may be located downstream from the sample cell 22 to evacuate air. As a result, leaks in the system can fall from the analyzer without pushing into the analyzer to minimize the risk of contaminating the internal components of the analyzer. In addition, unwanted products of unintended chemical reactions associated with the elastomer of the pump can be prevented from entering the sample cell 22.

In various embodiments, the flow rate through flow system 82 may be between 2 L / min and 10 L / min, although more and less flow rates may be used depending on the application. In one embodiment, the flow rate is between 3 L / min and 6 L / min. The pressure of the sample may be about 1 atm, but higher and lower pressures may be maintained depending on the application. In some embodiments, the sample cell can be operated at elevated pressures, such as up to 4 atm. The operating temperature of the sample cell may be between about 10 ° C. and about 40 ° C., but higher and lower temperatures may be maintained depending on the application. In one embodiment, the detection system can include a heating element that heats the sample to about 40 ° C. and about 180 ° C. In one embodiment, the temperature can be increased to about 150 ° C. to purify the device.

In various embodiments, the sample cell path length may be between about 5 m and about 12 m. The spacing between the field and objective surfaces can be limited by the gas sampling flow rate. In one embodiment, a 5.11-meter sample cell with 16 cm spacing and 32 passageways may have an internal volume of about 0.2 L. In another embodiment, for the same passage, a 20.3 cm gap with 32 passages may have a volume of about 0.4 L. In yet another embodiment, the 25.4 cm spacing can have a volume of about 0.6 L. Every at least 10 seconds a flow rate that can sufficiently supply a "fresh" ambient gas can be determined, but a smaller sampling rate can be achieved. In various embodiments, the flow rate (eg, between 2 L / min and 10 L / min) can be optimized to provide the optimum exchange rate of the gas. For example, in one embodiment, the exchange rate of gas is at least 80% at 20 second detection time intervals. In one embodiment, the exchange rate of gas is between about 80% and about 95% at 10 second detection time intervals.

The path length / NEA ratio can be used as a metric to quantify the sensitivity of the detection system, where the path length is the total beam path length of the sample cell measured in meters and NEA is the absorption units; AU) is the noise equivalent absorbance measured. If the sensitivity is limited by the non-systematic error of the detection system (also called random noise, eg detector and electronic noise), the detection limit may be inversely proportional to the path length / NEA ratio. For example, when the ratio is doubled, the detection limit of a particular sample in ppb or mg / m ³ units is halved. Therefore, this is a suitable quantification metric for sensitivity performance. This metric does not consider sensitivity improvements due to advanced sampling techniques such as, for example, gas pressurization and cold trapping.

Considering limiting system noise such as detector and digitization noise, the path length / NEA ratio can be optimized for various system configurations. Parameters that can be optimized include flow rate, sample cell volume, optical path length, number of passages through the sample cell, optical configuration, mirror reflectance, mirror reflecting material, and detector used. For example, an optimal detector is a detector with the highest D * value and speed (lower response time) within the constraints of size, cost and duration of use.

In the case of detector noise limited spectrometers, the sensitivity or path length / NEA ratio is proportional to the D * value. The detector bandwidth can determine the maximum scan rate and the maximum scan rate determines the maximum number of data averaging that can be performed within the allowed measurement period. In the case of a detector or electronic noise limited system, the sensitivity generally increases with the square of the average number of scans, or, for example, with the time to perform these scans. In one embodiment, the Stirling-cooled detector may provide a path length / NEA sensitivity ratio of at least ^1.5 × 10 ⁵ m / AU. DTGS detectors can provide a low cost alternative due to their low cost and unmanageable lifetime, but may have smaller D * values and may be slower.

The path length / NEA value can be determined by optimizing the distance between the field surface and the objective surface and the number of passages between these surfaces. 4 shows a graph of path length / NEA as a function of mirror reflection for various surface spacings, such as 6.3 inches (16.0 cm), 8 inches (20.3 cm) and 10 inches (25.4 cm). As shown in FIG. 4, the maximum path length / NEA value is generated in about 92 passages. However, in 92 passages, only 25% of the light is transmitted due to the reflection loss at the mirror surface. In one specific embodiment, the sample cell has a transmission between about 50% and about 60%. For the mirror reflectance of 98.5%, the 60% transmission corresponds to about 32 passages represented by the vertical lines in FIG. 50% transmission corresponds to about 48 passages. Table 1 shows an exemplary combination of parameters that provide a sampling system for detecting trace gas in a sample.

Table 1. An exemplary combination of parameters providing a sampling system for detecting trace gas in a sample.

system Surface thickness (cm) Passage Total path length (m) Path Length / NEA (m / AU) Cell volume (L) Flow rate ¹ (L / m) Flow rate ² (L / m) A 16.0 32 5.11 1.4 x 10 ⁵ 0.2 2 3 B 20.3 32 6.5 1.8 x 10 ⁵ 0.4 4 6 C 25.4 32 8.1 2.3 x 10 ⁵ 0.6 6 9 D 16.0  48 7.7 1.9 x 10 ⁵ 0.3 3 4.5 E 21.1 48 10.18 2.5 x 10 ⁵ 0.5 5 7.5 F 25.4 48 12.2 3.0 x 10 ⁵ 0.8 8 12

¹ Flow rate for gas exchange rate of 80% at 10 second intervals.

² Flow rate for gas exchange rate of 90% at 10 second intervals.

The path length / NEA ratio can be converted to the limit of detection of concentration (mg / m3 or parts per billion). The method used for this conversion is a comparison between the expected peak absorbance magnitude and the expected NEA value. Apparatus 10 may be used to detect trace amounts of substances such as sarin, starch, cattle, sulfur mustard, and VX nerve gas having a concentration of less than about 500 ppb. In various embodiments, the concentration may be between about 10 ppb and about 500 ppb, although higher and lower concentrations may be detected depending on the system and application. In some embodiments, the concentration may be between 5 ppb and about 50 ppb, depending on the species. For example, device 10 may comprise a trace amount of sarin having a concentration between about 8.6 ppb and about 30 ppb; Trace amount of wood with a concentration between about 12.9 ppb and about 39 ppb; Trace amount of wood with a concentration between about 7.3 ppb and about 22.8 ppb; Trace amount of sulfur mustard with a concentration between about 36.7 ppb and about 370.6 ppb; Or trace the amount of VX nerve gas having a concentration between about 12.9 ppb and about 43.9 ppb.

Sample of fresh phosphorus (gas renewal rate) gas refresh rate measure of the increase in gas supply in the cell is a gas Y detected, the "Z early detection system response times can be combined with the path length / NEA ratio X mg / m ³ (Or ppb) ". Detection system response time includes measurement time and calculation time (eg, about 5 seconds). Table 2 shows exemplary detection system response times for various drugs such as sarin, starch, cattle, sulfur mustard, and VX nerve gas.

Table 2. Example detection system response times for trace gases measured using the detection system of the present invention.

Trace gas Response time for 10 ppb Response time for 20 ppb Response time for 30 ppb Response time for 50 ppb Sarin 15.4 12 8.7 7.5 Tarmac 22.6 12.6 10.2 8.4 Shoman 13.7 9.6 8.3 7.2 Sulfur mustard 60 37.5 21.4 13.8 VX nerve gas 22.6 12.6 10.2 8.4

5 is a graph of trace gas concentration versus time using a step profile input (eg, trace gas enters a sample cell at the beginning of a measurement cycle). The measurement period "A" is the time at which data is to be collected and / or the interference degree is recorded. The calculation period "B" is when the interference is converted into a spectrum, and spectral analysis is performed to generate data used to determine alarm levels and / or concentration values.

6 shows a time line for a series of measurements. Drug 1 enters the sample cell and is detected using measurement period 1. Interference is analyzed for the calculation period 1. Drug 2 enters the sample cell during measurement period 1. If Drug 2 is sufficiently strong, it can be detected during the remainder of Measurement Period 1. If drug 2 is not detectable, it is detected during a subsequent measurement period, for example measurement period 2, and the interference is analyzed for the next calculation period, for example calculation period 2.

In one embodiment, readings may be time separated at fixed predetermined intervals. In various embodiments, the interval may be between about 1 second and about 1 minute, although smaller or larger intervals may be used, depending on the application. In some embodiments, the interval is about 5 seconds, about 10 seconds, or about 20 seconds. Therefore, the response time depends not only on this interval but also on the time that the drug can be detected by the detection system.

In various embodiments, the detection system may include external factors such as detection of trace gas, threat level, time of day, number of people in a room or building that may be affected by the drug, particular measurement application or scenario, or a combination thereof. It may adopt one or more parameters based on. For example, in high-threat conditions, smaller intervals may be used to minimize detection time and maximize the detectability of trace chemicals. In low threat situations, larger intervals can be used, which can maintain detection system life and reduce the likelihood of an alarm error (false positive or negative).

In addition, individual measurements above the threshold level for a particular drug can trigger the detection system to reduce the interval so that additional measurements can be made in a shorter time. In various embodiments, the first spectrum may be recorded at a first resolution or sensitivity. If contaminants are detected, the second spectrum can be recorded at higher resolution or sensitivity. In addition, the detector may have a standby mode operating at higher temperatures, thereby increasing its sensitivity. When triggered by an external factor, the temperature of the detector increases to improve its sensitivity.

In various embodiments, the detection system can vary the number of scans based on external factors or perceived threats. For example, an increased number of scans can be performed to improve the sensitivity of the detection system. In one embodiment, the detection system can operate at higher resolution while recording these additional scans. In one embodiment, each scan may include an increased number of average or individual scans.

In various embodiments, the detection system digitizes the low frequency region of the spectrum (eg, less than 1300 cm ⁻¹ ) so that it can only scan at higher speeds. Electronic filter or detector response functions may be used to remove higher frequency regions (eg, greater than 1300 cm ⁻¹ ) so that aliasing is prevented or minimized.

In some embodiments, the detection system can detect the presence of trace gas in a portion of the spectrum. The second portion of the spectrum can be analyzed to confirm the presence of the trace gas and / or to determine the concentration level of the trace gas.

In one embodiment, the detection system may be packaged as a compact, self-contained multiple gas analyzer. For example, the detection system may be a diagnostic tool for recording, charting, analyzing and reporting air quality. 7 and 8 illustrate exemplary detection systems for monitoring air quality, such as ambient air, for trace gases. Referring to FIG. 7, the detection system includes a housing 42 ', a first display 38', a second display 38 '', a gas inlet 46 ', a gas outlet 50', and external devices. Port 118 for connection.

Housing 42 ′ may be a three-dimensional rectangular box that includes top panel 122, side panel 126, and bottom panel 130 (shown in FIG. 8). The top panel 122 can be hingedly moved away from the side panel 126 so that the housing 42 'can be opened for service. The outer surface of the top panel 122 may include a first display 38 ′ and a second display 38 ″ attached or embedded therein. The first display 38 ′ may be, for example, a liquid crystal display (LCD) with a touch screen display. The first display 38 ′ may receive a command to operate the detection system and display a graphical user interface (GUI). The second display 38 ″ may be, for example, a light emitting diode (LED) display with a series of LEDs lit to indicate threat levels, alarm conditions, and / or detection system health conditions. For example, the second display 38 '' may include a first series of green, yellow, and red LEDs indicative of an alarm condition, and a second series of green, yellow, and red LEDs separated to indicate a sensor health condition. have. In various embodiments, the housing 42 'may define a hole for intake of ambient air. The aperture can be used to introduce a sample of gas into the flow system for detection in the sample cell.

8 shows the interior of the top panel 122 and the bottom panel 130 when the top panel 122 is hingedly moved to open. The bottom panel includes an inner chassis that includes an optical box 134 for the housing optical component. The optical box 134 may be formed of an aluminum shell (eg, 6061-T6). In one embodiment, the optical box 134 is a sealed box. As illustrated in FIG. 8, the optical box 134 includes a source 14 ', an interferometer 18', a sample cell 22 ', a detector 30', a parabolic mirror 54 ', a first collapsible mirror. 58 ', second fold mirror 62', oval mirror 66 ', objective 74', and field surface 78 '. The optical box 134 also includes a flow system that includes a valve 138 that regulates gas flow, a pressure sensor 98 ', a pump 106', and a gas line 110 and accessories 142 for connection. It may include. Power supplies 146 and fans 150 for various components may also be attached to the bottom panel 130. The detection system can be operated in stationary air and the fan 150 can maintain the internal temperature of the system. The bottom panel 130 also includes a connector 154 for interfacing with the top panel 122.

As illustrated in FIG. 8, top panel 122 may include an electronic component attached thereto. For example, the top panel 122 may include a data acquisition module 158, a mirror motion control module 162, a single board computer 166, a power distribution module 170, and a hard drive 172. The data acquisition module 158 may include a preamplifier, an analog-to-digital converter, and a data acquisition board. The preamplifier may amplify the analog signal received from the detector 30 '. The analog signal can be converted into a digital signal using an analog to digital converter. The data acquisition board may be a Netburner processor board available from Netburner (San Diego, Calif.). Single board computer 166 may be a ready-to-use PC motherboard that drives Windows and provides a GUI to the user.

The power distribution module 170 may process and distribute power to other modules in the system and may implement health and condition sensors used to monitor the functionality of the detection system. For example, the power distribution module 170 may distribute AC power to the system power supply 146 and the fan 150, and may include a temperature controller 174, such as Dwyer Instruments, Inc. ; Love controls, available from Michigan City, Indiana. The power distribution module 170 also monitors sample cell pressure, differential pressure across the air filter, sample cell temperature, and detector temperature, A / D converts the output, and passes the results back to the single board computer 166. do. The power distribution module 170 may also control the cooler motor of the Stirling cooled detector according to instructions from the single board computer 166. Upper panel 122 may also include a sample cell temperature transmitter.

Data processing may be performed using a module attached to the top panel 122 that may enable real-time analysis of the data. The spectral library can include spectral fingerprints between about 300 and about 400 gases, but more gases can be added as the spectrum is recorded. Data processing can be performed in standard computer programming languages such as MATLAB or C ++. The recorded spectrum can be passed to MATLAB for spectral post-processing to calculate gas concentration, remaining spectrum, and / or false alarm rate. In various embodiments, the detection system may be operable to have fewer than six false alarms per year. False alarms can be due to noise, anomalous spectral effects, analysis code, model errors, errors in the spectral library, or unknown interference.

Computer software can run on a Java-based platform with graphical remote control capabilities. The computer software can integrate standard services, including an Ethernet interface to a client computer that can be remotely located from a user login, web-based GUI, alarm triggering, and / or detection system. Computer software can perform remote health and control diagnostics. In addition, port 118 may be used to connect a system capable of performing data processing and data analysis to a standalone computer.

The housing 42 'is designed to withstand 50G shock. In one embodiment, the housing 42 'may have a length of about 406 mm and a width of about 559 mm. The mass detection system may be about 20 kg. The housing 42 'may be mounted on a wall, a mobile cart, or a cart and may include a handle (not shown) for transporting manually or using a mechanical lifting device. In one embodiment, the housing may be mounted as part of a building air treatment system. If the detector detects the presence of contaminants, remedial action can be taken to account for the contaminants. For example, the alarm may sound to evacuate the building, or the air flow in the air treatment system may increase to remove contaminants from the public area or to reduce trace gas to an acceptable level.

In various embodiments, the detection system may operate at elevated temperatures to purify the system in case of contamination. The system may be configured such that the sample cell and flow system can be heated to a temperature between about 150 ° C. and about 200 ° C. while maintaining the remaining components below about 70 ° C., including electronic and optical components. Can be. For example, components heated to about 150 ° may be insulated from the surrounding components to prevent damage to the electronic components and rearrangement or damage of the optical components. Operation of the sample cell and flow system at elevated temperatures can accelerate the removal of contaminants. In one embodiment, the detection system can operate while the system is being cleaned, so that the progress of the cleaning can be monitored. In one embodiment, the detection system is purged with nitrogen gas or ambient air during purging. The gas may comprise moisture (eg, about 30% or more relative humidity). In various embodiments, the system may be purged in less than about 2 hours, ready to return to service.

In one embodiment, the concentration of contaminants in the detection system may be determined, and if the concentration of contaminants exceeds the contamination value, at least the sample region may be heated to a purge temperature to remove the contaminants. The concentration of contaminants can be monitored while heating the sample region, and heating can be reduced or stopped when the concentration of contaminants reaches a purification value. The contamination value may be a concentration of material that indicates the performance of the detection system. The purge value can be the concentration of material at which the detection system can operate without being affected by contaminants.

In various embodiments, the sample cell of the detection system can operate at elevated pressure. The path length / NEA ratio may not change, but the sensitivity of the detection system may be improved as more of the trace gas sample is present in the sample cell with the same path length. It may also generate a larger absorption signal relative to the baseline. The pressure can be raised by increasing the flow rate while keeping the sample cell volume unchanged.

The field and objective surfaces can be fixedly mounted so that their position remains substantially unchanged when the pressure rises. For example, the field and object surfaces may be mounted on rods to secure these surfaces. In addition, the sample cell may be substantially sealed. The objective and field surfaces in the sample cell can be wrapped with sample gas such that positive pressure can be applied to each of the back side of the field and objective surfaces to prevent deformation at elevated pressures. In various embodiments, the pressure may be between 1 atm and about 10 atm. In one embodiment, the pressure is 4 atm.

In some embodiments, signals at two separate pressures can be measured and can take the ratio of these signals. The ratio of signals may remove baseline noise, improve sensitivity, and / or increase the amplitude of the absorption profile of the trace gas with respect to the baseline signal.

The first signal of the radiation beam propagating through the sample of ambient air at a first pressure in the sample cell is measured. The sample cell is pressurized with ambient air up to the second pressure. A second signal of the radiation beam propagating through the sample of ambient air is measured at the second pressure in the sample cell. The first and second signals can be combined to determine a signal indicative of the presence of trace gas. For example, the signals can be combined to obtain an absorption profile for trace gas. In one embodiment, the radiation beam may comprise an interfering signal. The absorption profile for the trace gas can be determined from the interfering signal. In one embodiment, the first pressure is about 1 atm and the second pressure is between about 1 atm and 10 atm. In one specific embodiment, the first pressure is about 1 atm and the second pressure is about 4 atm.

In various embodiments, the first signal is used as the baseline signal for the second signal because the optical alignment of the sample cell is maintained substantially unchanged when the pressure increases. In some embodiments, the baseline signal is measured and used as the baseline signal for both the first signal and the second signal.

In various embodiments, the flow system may include a cold finger that collects by cooling the gas sample of interest below its saturation temperature. Many volatiles condense at or below -75 ° C. In one embodiment, a cryogenic cold trap is formed at the gas outlet from the sample cell. After a designated time period or collection period, the trapped gas or the trapped gases may be rapidly evaporated by heating or "flashed" back into the sample cell, and spectral measurements may be made. This technique can increase the target gas amount by approximately size or two while keeping the sample cell at atmospheric pressure. In one embodiment, continuous flow measurements may be performed after the time interval, such as about every 10 seconds, while allowing instantaneous delivery at longer time intervals.

In various embodiments, the detection system may include a long pass filter. The noise from the A / D converter can be the same size as the noise from the detector. The inclusion of a long pass filter can block higher wavenumber ranges and improve the reduction by reducing the digitizer dynamic range requirement through a reduction in the interference centerburst size. Dynamic range of the detector without optical filter of about 600 cm ^-1 and about 5000 cm ^- can be between ^1. Because a large number of toxic substances aiming detectable to less than 1500 cm ^-1, 1500 cm ^-1 High spectrum than by using the long-wave pass filter in order to obtain the sensitivity can be eliminated. For example, for a commercially available standard long wave filter with a cutoff at about 1667 cm ⁻¹ , the gain in path length / NEA ratio may be from about 20% to about 30%. In addition, using a long pass filter allows the detector to operate at a higher gain, for example the highest gain achievable with a particular detector, thereby improving the signal-to-noise ratio of the detection system. In various embodiments, low sensitivity detectors, such as MCT detectors or DTGS detectors, may be used to record the spectrum in the higher frequency region.

While the invention has been particularly shown and described with respect to particular embodiments, it should be understood that various changes in form and detail may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.

In accordance with the present invention, trace amounts of chemical warfare agents, toxic industrial drugs, and other trace compounds that can be found in ambient air can be detected.

Claims (28)

Trace gas measuring device, A source of a first radiation beam; An interferometer for receiving the first radiation beam from the source and forming a second radiation beam comprising an interference signal; In optical communication with the interferometer, the concave reflective field surface having a concave reflective field surface at the first end of the sample cell and a substantially spherical concave reflective object surface at the second end of the sample cell in opposition to the field surface; The object plane has a sample with a cylindrical component that increases focus agreement in at least one plane to maximize throughput of the second radiation beam propagating through the sample cell through multiple reflections in each of the field plane and the object plane. Cell; A flow mechanism forming a flow of a sample of gas through the cell sample; A cooled detector in optical communication with the sample cell, the cooled detector receiving an interference signal propagating through a sample in the sample cell; A processor in electrical communication with the cooled detector, the processor determining from the interference signal an absorption profile for the trace gas in the sample; And And a housing in which the source, the interferometer, the sample cell, the cooled detector, and the processor are disposed. The method of claim 1, The trace gas having a concentration of less than about 500 ppb. The method of claim 2, The trace gas having a concentration between about 10 ppb and about 50 ppb. The method of claim 1, The housing being portable and defining a hole for intake of ambient air containing a sample of the gas, the hole in fluid communication with the sample cell. The method of claim 1, The housing is trace gas measurement device mounted to the building air handling system. The method of claim 5, And an alarm to alert the presence of contaminants in the air treatment system. The method of claim 1, Wherein said sample cell has a volume of less than about 0.8 liters. The method of claim 1, And a sample of said gas flows through said sample cell at a flow rate greater than about 3 liters per minute. The method of claim 1, And the sample cell comprises a path length between about 5 meters and about 12 meters. The method of claim 1, The sample cell having a gas exchange rate between about 80% and about 95% at a time interval of about 10 seconds. The method of claim 1, Sample of the gas is trace gas measuring device comprising a chemical agent, a toxic inorganic compound, or a toxic organic compound. The apparatus of claim 1, wherein the device has a response time of less than about 20 seconds for about 50 ppb of at least one of sarin, starch, cattle, sulfur mustard, and VX. 10. The apparatus of claim 1, further comprising a heating element disposed within the housing for heating at least the sample cell to a temperature between about 40 ° C and about 180 ° C. As a method of optically measuring trace gas, Providing a portable absorption spectrometer comprising a sample cell comprising a field surface at a first end and an object surface at a second end in opposition to form a folded path; Flowing a sample of ambient air through the cell sample; And In order to maximize the throughput of the radiation beam propagating within the sample cell to detect trace gas with a concentration of less than about 500 ppb in the sample of ambient air, the volume of the sample cell and the number of passages of the radiation beam in the folded path are maximized. Optically measuring a trace gas comprising the step of optimizing. The method of claim 14, The field surface comprises a concave reflective surface, the object surface comprising a substantially spherical concave reflective surface, the object surface having at least one to maximize throughput of the radiation beam propagating through the folded path of the sample cell A method of optically measuring a trace gas with a cylindrical component that increases focus agreement in the plane of the plane. The method of claim 14, Determining an absorption profile for the trace gas from an interference signal propagating through the sample in the sample region. The method of claim 14, Measuring a first absorption spectrum at a first resolution to detect the trace gas; And And measuring the second absorption spectrum at a higher resolution. The method of claim 14, Measuring a first absorption spectrum with a first sensitivity to detect the trace gas; And And optically measuring the trace gas further comprising measuring a second absorption spectrum with a higher sensitivity. The method of claim 14, Flowing the sample such that the sample region has a gas exchange rate between about 80% and about 95% at time intervals of about 10 seconds. The method of claim 14, Heating the sample region to a temperature between about 40 ° C and about 180 ° C. As a method of optically measuring trace gas, An absorption spectrometer comprising a substantially enclosed sample cell, wherein the sample cell comprises a field surface at a first end and an object surface in opposition to a second end to direct a radiation beam through the sample cell. step; Measuring a first signal of a radiation beam propagating through a sample of ambient air at a first pressure in the sample cell; Pressurizing the sample cell with ambient air until a second pressure is reached; Measuring a second signal of a radiation beam propagating through a sample of ambient air at a second pressure in the sample cell; And And optically measuring the trace gas combining the first signal and the second signal to determine a signal indicative of the presence of trace gas. The method of claim 21, The field surface comprises a concave reflective surface, the object surface comprising a substantially spherical concave reflective surface, the object surface having at least one to maximize throughput of the radiation beam propagating through the folded path of the sample cell A method of optically measuring a trace gas with a cylindrical component that increases focus agreement in the plane of the plane. The method of claim 21, Combining the first signal and the second signal to determine an absorption profile for the trace gas. The method of claim 21, Wherein the radiation beam optically measures a trace gas comprising an interfering signal. The method of claim 24, Determining an absorption profile for the trace gas from the interference signal propagating through the sample in the sample cell. The method of claim 23, wherein Increasing the amplitude of the absorption profile of the trace gas relative to a baseline signal by applying pressure to the sample cell. A method of removing contaminants from an optical system, Determining the concentration of contaminants in at least one sample region of the absorption spectrometer; If the concentration of contaminant exceeds a contamination value, heating the sample region to a purge temperature to remove the contaminant; Monitoring the concentration of the contaminant while heating the sample region; And Reducing or stopping heating of the sample area when the concentration of the contaminant reaches a purification value. Trace gas measuring device, An interferometer receiving a first radiation beam from a source and forming a second radiation beam comprising an interference signal; A sample cell in optical communication with the interferometer; A flow mechanism forming a flow of a sample of gas through the cell sample; A module for heating at least the sample cell; A detector in optical communication with the sample cell, the detector receiving an interference signal propagating through a sample in the sample cell; A processor in electrical communication with the detector and the module; The processor determines the concentration of contaminants in the sample from the interference signal and heats the sample cell to a purge temperature to remove the contaminants when the concentration of contaminants in the sample cell exceeds a contamination value. A signal to monitor the concentration of the contaminant while the module heats the sample cell and to signal the module to reduce or stop heating of the sample cell when the concentration of the contaminant reaches a purification value. Gas measurable device.

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